First of all: Thx to all of you for developing arduino and sharing your knowledge. (Big Fan)
I have a challenging sensor problem:
I have to sense the rotation on 3 DC gear motors - lame and easy problem at the beginning BUT everything is very tiny.
They are the motors for a motorized CCTV lens.
Have a look on the attached images to get an idea. (The scale is in mm)
The thing is, there should be a higher resolution than just one tick per rotation. --> counting the teeth of the gearwheel would do a perfect job.
I have thought on three different solutions:
- using a tiny SMD photointerrupter like this on: http://de.rs-online.com/web/p/photointerrupter/6165670/
Here trying to accurately place it, that one passing teeth of the gear creates a usable signal.
Do you have experience in using them with such small objects (the teeth of the wheel). To increase contrast it would be good to paint them black and do some additional signal processing. Can I get an analog signal from them?
- mechanically attaching a rotary encoder (with an additional gearwheel) Main problem is the lack of space. I once had one from a very old mechanical computer mouse. Does anyone know where I can by such things in small?
- trying to resolve the motion of the motor rotor by simply attaching a hall-effect sensor on the outside of the DC motor. (I have no experience in this. It is probably challenging because the magnetic changes are quite weak on such small motors)
Pro on this solution: great resolution because directly the higher frequency signal before the gearbox is grabbed.
Thanks in advance for your ideas.